a. Field of the Invention
This invention relates to methods for making flame-retardant, fiber-forming polyester polymers.
B. Prior Art
It is known to use germanium dioxide as a catalyst in a polycondensation reaction to produce polyesters. Usually, the germanium dioxide is added to the reaction mixture with a glycol, such as ethylene glycol. Unfortunately, the crystalline germanium dioxide has a very low solubility in the glycol, resulting in undissolved catalyst which remains in the polymer. The undissolved catalyst particles may easily result in undesirable physical properties in fibers made from the polymer. Also, low catalyst concentrations result in longer reaction times. Further, this catalyst tends to promote the formation of undesirable side products such as diethylene glycol.
Other catalyst, such as zinc acetate, arsenic oxide and glycoloxide and tetrabutyl titanate, have been used to prepare polyesters. These catalysts usually require unduly long polymerization times and frequently result in badly discolored polymers. Apparently, conventional catalysts complex with phosphine oxides.
It has been found that the use of the germanium dioxide/tetraalkyl ammonium hydroxide catalyst of this invention results in faster condensation rates, lower formation of undesired side products and insures superior whiteness of fibers made from the polymer prepared by this invention.